View Full Version : [all variants] Proxy ARP not working

December 8th, 2010, 09:30 PM
I'm having an issue on multiple Lucid boxes where I can't get proxy ARP to work. This is to be used in conjunction with openswan IPSec. I've enabled forwarding and disabled sending/accepting ICMP redirects for each interface as per openswan's requirements. I've added the proxy arp lines for all, default, eth0, and lo to sysctl.conf:

net.ipv4.conf.eth0.proxy_arp = 1I then connect the IPSec client, and I have connectivity to the server. When I try to ping (or otherwise access) something else on its subnet, I reach the intended target, but then it ARPs for the sending machine, and the Ubuntu server doesn't respond to the ARP.

I have an ARP entry that looks like this, added via arp -s -D eth0 -i eth0 pub:

Address: (the correct virtual IP for the client)
HWtype: *
HWaddress: <from_interface>
Flags Mask: MP
Iface: eth0

Best I can tell, everything is in order... I can listen in with wireshark on the server and see that it's receiving the ARPs, but I can't get it to respond to them. What am I missing?

December 11th, 2010, 03:50 PM

Edit: I read somewhere that, if proxy_arp is enabled, Ubuntu will automatically send ARP replies for any host or network to which it's routing. I tried adding a route to the host, but it still isn't responding to ARPs for the required address (verified with tcpdump).